U.S. patent number 5,957,202 [Application Number 08/815,653] was granted by the patent office on 1999-09-28 for combination production of shallow heavy crude.
This patent grant is currently assigned to Texaco Inc.. Invention is credited to Wann-Sheng Huang.
United States Patent |
5,957,202 |
Huang |
September 28, 1999 |
Combination production of shallow heavy crude
Abstract
Techniques are disclosed for the safe production of shallow
heavy oil sands which substantially reduce the probability of
surface steam breakthrough. A pattern of injection wells and
producing wells are drilled through the overburden into a
relatively shallow heavy oil producing zone. Firstly the injection
wells and the producing wells are cold produced for a combination
of heavy oil and sand by use of a progressive cavity pump or the
like. Then steam push-pull is used on both the injectors and
producers until heavy oil production becomes uneconomical. Finally,
low pressure steam is continuously injected into the injection well
and heavy oil continuously produced from the producing wells.
Inventors: |
Huang; Wann-Sheng (Houston,
TX) |
Assignee: |
Texaco Inc. (White Plains,
NY)
|
Family
ID: |
25218421 |
Appl.
No.: |
08/815,653 |
Filed: |
March 13, 1997 |
Current U.S.
Class: |
166/272.3;
166/272.7 |
Current CPC
Class: |
E21B
43/24 (20130101); E21B 43/30 (20130101) |
Current International
Class: |
E21B
43/16 (20060101); E21B 43/30 (20060101); E21B
43/24 (20060101); E21B 43/00 (20060101); E21B
043/24 () |
Field of
Search: |
;166/263,272.3,272.7,303 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Neuder; William
Attorney, Agent or Firm: Gibson; Henry H. Beard; William
J.
Claims
I claim:
1. A method for producing heavy crude oil from shallow formations
while reducing the probability of surface steam breakthrough,
comprising the steps of:
drilling and completing a predetermined pattern of injection wells
and producing wells through the overburden over a shallow heavy oil
producing zone and into the producing zone;
cold producing a combination of heavy oil and sand from the
producing zone by use of a heavy oil pumping means for a
predetermined period of time, thereby enlarging the borehole
effective diameter in the producing zone in the vicinity of the
well bores of said injection and producing wells;
injecting low pressure steam into said injection wells and said
producing wells simultaneously for a predetermined period of time,
to heat and lower the viscosity of the heavy oil near the wellbores
of said injection and producing wells, stopping said steam
injection and producing a sand and lowered viscosity heated heavy
oil from said injection wells and said producing wells
simultaneously until the reduced viscosity heavy oil is essentially
produced and then repeating this push-pull cycle of low pressure
steam injection and heavy oil and sand production until the oil
production becomes uneconomical; and
injecting low pressure steam into said injection wells and
producing heated heavy oil and sand from said producing wells
continuously.
2. The method of claim 1 wherein the injection wells are drilled
vertically through the producing zone and the producing wells are
drilled horizontally near the bottom extent of the producing
zone.
3. The method of claim 1 wherein the wells are drilled in a five
spot pattern with the injection wells located centrally in the five
spot.
4. The method of claim 3 wherein the producing wells are drilled
with their horizontal wellbores directed along the periphery of the
five spot pattern.
5. The method of claim 3 wherein the producing wells are drilled
with their horizontal wellbores located diagonally toward the
central well of the five spot pattern.
6. The method of claim 1 wherein the step of injecting low pressure
steam is performed by injecting steam at a pressure of less than
250 PSI.
7. The method of claim 6 wherein the step of injecting low pressure
stem is preformed by injecting steam at a pressure of less than 100
PSI.
8. The method of claim 1 wherein the producing wells are drilled
horizontally near the bottom extent of the producing zone and are
perforated along their entire horizontal extent.
9. The method of claim 1 wherein the step of cold producing a
combination of heavy oil and sand by use of a heavy oil pumping
means is performed by use of a jet pump.
10. The method of claim 1 wherein the step of cold producing a
combination of heavy oil and sand by use of a heavy oil pumping
means is performed by use of a screw pump.
11. The method of claim 1 wherein the step of cold producing a
combination of heavy oil and sand by use of a heavy oil pumping
means is performed by use of a progressive cavity pump.
12. The method of claim 1 wherein the wells are drilled in a seven
spot pattern with injection wells located centrally in the seven
spot pattern.
13. The method of claim 12 wherein the producing wells are drilled
with their horizontal wellbores directed along the periphery of the
hexagon of the seven spot pattern.
14. The method of claim 12 wherein the producing wells are drilled
with their horizontal wellbores oriented radially toward the
central well of the seven spot pattern.
Description
FIELD OF THE INVENTION
This invention relates to oil and gas reservoir production
techniques and, more particularly, to techniques for the production
of heavy oil in shallow reservoirs which avoid potentially damaging
environmental effects caused by surface steamflood
breakthroughs.
BACKGROUND OF THE INVENTION
In some areas of the world there are really large deposits of very
viscous or heavy crude oils or tar sands which are located near the
surface of the earth. The overburden in such areas may be as little
a two to three hundred feet. In such cases the overburden is thick
enough to effectively prevent the surface strip mining of the heavy
oil deposit, but it may be, like the heavy oil sand itself, loosely
consolidated and not, in effect, a good sealant of the heavy oil
sand from the surface.
One especially effective technique used in the past for producing
such heavy tar or oil sand formations has been steam flooding of
the formation. In steam flooding a pattern of wells is drilled
vertically through the overburden and into the heavy oil sand,
usually penetrating the entire depth of the sand. Casing is put in
place and perforated in the producing interval and then steam
generated at the surface is pumped under relatively high pressure
down the casing and into the heavy oil formation. In some instances
the steam may be pumped for awhile into all of the wells drilled
into the producing formation and, after the heat has been used to
lower the viscosity of the heavy oil near the wellbore then the
steam is removed and the heated, lowered viscosity, oil is pumped
to surface, having entered the casing through the perforations.
When the heat has dissipated and the heavy oil production falls
off, the production is closed and the steam flood resumed. Where
the same wells are used to inject steam for awhile and then for
production, this technique has been known as the huff and puff
method or the push-pull method.
In other instances, some of the vertical wells penetrating the
heavy oil sand are used to continuously inject steam while others
are used to continuously produce lower viscosity oil heated by the
steam. Again, when heavy oil production falls off due to lack of
heat, the role of the injectors and producers can be reversed to
allow injected steam to reach new portions of the reservoir and the
process repeated.
In all of these production techniques, the steam flood is performed
at a relatively high pressure (hundreds to over one thousand pounds
per square inch or PSI) so as to allow it to penetrate as deeply
into the production zone as possible. This can lead to severe
environmental problems if the overburden is relatively incompetent
which could be penetrated by the heated crude oil, water or steam
pumped into the injection wells. Steam breakout to the surface has
occurred on more than one occasion in the past when using such
production techniques. This can result in serious environmental
contamination, particularly if the steam breakout occurs as geysers
of hot water and lowered viscosity crude oil onto the earth's
surface, as has occurred in the past.
Accordingly, it would be very desirable to develop techniques for
effectively producing heavy oils in shallow reservoirs in which
steam flooding could be used, but with lower injection pressures so
as to avoid surface breakout. The present invention provides
production techniques for use in relatively thin or relatively
thick heavy oil sand production zones located at shallow depths.
The techniques of the present invention are both safe and efficient
in recovering the heavy oil from shallow formations and in lowering
the required steamflood pressures so as to minimize the potential
of surface steam breakthrough.
BRIEF DESCRIPTION OF THE INVENTION
The techniques of the present invention for safely producing
shallow deposits of heavy crude oil basically comprises four steps.
The steps may differ slightly depending upon the thickness of the
heavy crude production zone, but essentially are as follows: (For a
five spot pattern)
1. Drill a vertical injection well and four horizontal producing
wells in a five spot pattern.
2. Cold produce heavy crude from both the injector and the
producers by producing sand and oil simultaneously using a jet
pump, screw pump or a progressive cavity pump.
3. Inject steam into the injection well and the four producing
wells at relatively low pressure (less than 100 PSI rather than
hundreds of PSI) for a predetermined time. Then produce heavy crude
and sand from the injection well and the four producers again. Low
pressure injection is achievable because "wormholes" have been
created as a result of the initial sand and oil production. The
reservoir permeability then becomes much higher. When production
falls off due to heat loss reverse the process and again inject low
pressure steam into the four horizontal production wells and the
injection well for a predetermined period. This cycle is repeated
in the huff and puff or push-pull manner until the oil production
rate becomes uneconomical.
4. Inject low pressure steam continuously into the vertical
injection well and produce oil and sand from the producing
wells.
The invention may best be understood by the following detailed
description thereof when taken in conjunction with the accompanying
drawings. The drawings are intended as illustrative and not as
limitative of the invention.
BRIEF DESCRIPTION OF THE INVENTION
FIG. 1A schematically shows a five spot pattern for use with
relatively thin shallow heavy oil sands according to the invention;
and
FIG. 1B schematically shows a five spot pattern for use with
relatively thicker shallow heavy oil sands according to the
invention.
FIG. 2A schematically shows a seven spot pattern for use with
relatively thin heavy oil sands.
FIG. 2B schematically shows a seven spot pattern for use with
relatively thicker heavy oil sands.
DETAILED DESCRIPTION OF THE INVENTION
The following descriptions of the technique of the present
invention will be described with reference to a particular well
placement pattern known as the "five spot" for its resemblance to
the five on a pair of dice. However, it will be appreciated by
those of skill in the art, that the techniques of the present
invention are equally applicable to the safe recovery of shallow
heavy crude oil deposits using other placement patterns of
injection and/or producing wells, if desired.
Traditionally, the most effective method in recovering heavy oil is
by the use of steam floods. Other methods can either recover only
small portions of the oil in place or, in some instances, not
recover any oil at all. In the case of a shallow heavy oil deposit,
the use of high pressure steam injection runs the risk of possible
surface breakout of steam and/or steam/water/oil emulsions because
of the high injection pressures (several hundreds to over a
thousand PSI). In the techniques of the present invention this is
avoided because, while using the steam flood techniques basically,
only low injection pressures are necessary for the steam injection
for reasons which will become apparent as the techniques are
described with more particularity.
Referring to FIGS. 1A and 1B, schematic views (from above the
earths surface) are shown of the recovery techniques of the present
invention. FIG. 1A shows a five spot pattern having the central
well as an injector well and being oriented vertically. The four
corner wells are drilled horizontally (i.e. parallel to the earth's
surface) near the bottom of the producing zone and with their well
bores oriented along the sides of the "five spot" square as
shown.
FIG. 1B shows a five spot pattern in which the center well is
drilled vertically and is an injection well, again perforated
across the entire production zone. The corner wells of the pattern
are again drilled horizontally, but in this instance with their
well bores oriented diagonally in the pattern toward the center
well. Again the horizontal wells are kept as near the bottom plane
of the producing zone as possible and all are perforated all along
their horizontal extent. The well placement pattern of FIG. 1A is
particularly useful in accordance with concepts of the present
invention in production sand intervals which are relatively thin,
i.e. 30 feet thickness of less. The pattern of FIG. 1B is
particularly useful in relatively thicker production sand intervals
of greater than 30 feet in thickness.
FIG. 2A shows a "seven spot" pattern having the central well
drilled as an injector well and being oriented vertically. There
are six corner wells which are drilled horizontally near the bottom
of the producing zone. The wellbores of the corner well are
oriented along the sides of the seven spot hexagon as shown.
FIG. 2B shows a seven spot pattern in which the center well is
drilled vertically and is an injection well. This well is, again,
perforated across the entire production zone. The corner wells of
this pattern (at the hexagon corners) are again drilled
horizontally, but in this instance their well bores are oriented
radially toward the center well in the pattern. These wells again
are kept as near the bottom plane of the producing zone and all are
perforated along their entire horizontal extent. The well placement
pattern of FIG. 2A is most useful in relatively thin producing
intervals while the pattern of FIG. 2B is more useful in thicker
production sands.
The techniques of the present invention may differ slightly
according to the thickness of the producing zone as outlined above.
However, these techniques may be broken down into four major steps.
These steps are:
(1) Drill vertical injection wells and horizontal production wells
into the production zone as described above with respect to FIGS.
1A and 1B.
(2) Produce both oil and sand from both the production wells and
injection wells cold without the use of steam. Cold production can
be achieved by producing oil and sand simultaneously using either a
progressive cavity pump, a screw pump or a jet pump. Typically in
12.degree. API heavy oil, very high sand content (40% to 50% by
volume) is produced during the first few weeks of production. Sand
production then typically declines slowly to about 10% over a
period of about 100 days. Continued small percentages of sand
production are associated with the oil production. It has been
found that from 3% to 8% of the total oil in place can be produced
from this commingled oil and sand production.
(3) When production from step (2) becomes not economical, start low
pressure (about 250 PSI) steam injection in both the injection
wells and the producing wells in the pattern. Use the push-pull or
huff and puff technique wherein the steam is injected for a
predetermined period of time and then stopped and oil production is
begun on both injectors and producers until the production rate is
un-economical and then the steam injection cycle is repeated, etc.
Because of the initial cold production of oil and sand in step
(2) the cavity around the well bores becomes much larger than the
casing diameter. Very likely there are channels left behind in the
formation by the migrating sand. As a result steam can be injected
without a large pressure drop during the steam injection period.
After a soaking period, more oil and sand are produced by use of
the screw pump, progressive cavity pump, etc. and even more
channels and a larger effective well bore are created. This steam
push-pull cycle is repeated until the oil production rate becomes
uneconomical.
(4) Inject steam into the injection well only and produce oil and
sand from the producing wells. By this point, the well bores have
become so large that no significant pressure differential is
required to inject the steam. Because of the use of only low
pressure steam the possibility of steam breakout at the surface is
reduced or eliminated. The horizontal producing wells, because of
their large drawdown capability, further reduce formation pressure.
The strong pressure sink created and enforced by sand channels left
behind by the migrating sand, drastically reduce reservoir pressure
efficiently through the reservoir. The horizontal wells can provide
a line pressure sink in the formation so that the areal efficiency
of the continuing steam flood is increased.
The techniques described above may make other alternative
arrangements apparent to those of skill in the art. For example,
the injection wells could be drilled horizontally also, as long as
the operational sequence proceeds as described through the oil and
sand cold production stage to produce the enlarged well borehole
generated by this process. Also, as previously described, other
than five spot or seven spot well placement patterns could be used
if desired. Accordingly the aim of the appended claims is to cover
all such changes and modifications that fall within the true spirit
and scope of the invention.
* * * * *